Apparatus for stripping residual solvent from polymer pellets

Abstract

Apparatus for continuous stripping of residual volatiles from polymer pellets, having their surfaces wet with water, by the use of an upwardly moving flow of steam through a downwardly moving column of wetted polymer pellets, moving in plug-flow, which minimizes back-mixing. The apparatus operates with substantially less energy requirements than those of the prior art, and air pollution is eliminated since the apparatus recovers the volatiles by condensing the steam containing the stripped volatiles and recovering them. In the preferred case, back-mixing of the pellets at the bottom of the column is minimized by feeding the pellets to the top of the column over a deflector having a circular base approximately one-half the diameter of the column and by further deflecting the pellets at the base of the column from the center axis toward the wall of the inverted conical base of the column.

We claim: 
     
       1. An apparatus suitable for removing residual volatiles from solid pellets which consists essentially of the combination of: a. a vertical cylindrical top section having a length-to-diameter ratio greater than about 3:1 above,   b. an inverted conical bottom reducing section,   c. a first conical pellet distributor axially centered with its apex just below and adjacent to a pellet inlet at the center of the top of the column, the circular horizontal base of said distributor having a diameter of about one-half the diameter of the cylindrical column,   d. a second pellet distributor located within the conical bottom reducing section, said second pellet distributor having the form of two cones joined at their bases, said cones haing included angles approximately equal to the included angle of the conical reducing section at the bottom of the column and said second distributor being axially centered with its upper apex at the level of the knuckle joining the cylindrical top portion and the conical bottom reducing section of the column leaving an annular passage between the distributor the wall of the conical reducing section, said second pellet distributor containing circumferentially distributed means in its top portion for passing gas from the interior to the exterior,   e. gas inlet means leading to the interior of the second pellet distributor,   f. gas inlet means circumferentially evenly spaced near and around the top of the inverted conical reducing section of the column,   g. a pellet outlet at the base apex of the inverted conical reducing section of the column said first conical pellet distributor (c) is hollow and affords means in its conical surface to permit liquid to flow through from the exterior to the interior of the hollow distributor, and means leading from the interior of said first distributor to a liquid outlet outside the column and in which the pellet inlet at the center of the top of the column is connected to a liquid S- seal having a mixing tee at its further end with an inlet for liquid and an inlet for solid pellets, and   h. a gas outlet in the top of the column.   
     
     
       2. The apparatus of claim 1 in which the included angle of the bottom inverted conical reducing section is between 20° and 60°.